package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MapperStatement;

import java.lang.reflect.*;
import java.util.List;

/**
 * @author ADMIN
 * @date 2021/3/21 18:49
 */
public class DefaultSqlSession implements SqlSession {
    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }


    @Override
    public <E> List<E> selectList(String statementId,Object... params) throws Exception {
//将要去完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MapperStatement mapperStatement = configuration.getMapperStatementMap().get(statementId);
        List<Object> query = simpleExecutor.query(configuration, mapperStatement, params);

        return (List<E>) query;
    }

    @Override
    public <T> T selectOne(String statementId, Object... params) throws Exception {
        List<Object> objects = selectList(statementId, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }


    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
//使用jdk的动态代理为dao接口生成代理对象,并返回
        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                //底层还是去要执行jdbc代码 //根据不同的情况来调用selectOne 还是selectList
                //准备参数 1, statmentId :sql语句的唯一标识 :namespace.id = 接口全限定名.方法名
                //方法名
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();
                String statmentId = className + "." + methodName;
                //准备参数2 :params
                //获取返回方法的返回值
                Type returnType = method.getGenericReturnType();
                //判断是否进行了类型参数化
                if (returnType instanceof ParameterizedType) {
                    return selectList(statmentId, args);
                }

                return selectOne(statmentId, args);
            }
        });
        return (T) proxyInstance;
    }
}
